Today, not only electronic apparatuses dedicated to shooting such as a digital camera, but also portable intelligent electronic apparatuses such as a smart phone, a notebook computer and a tablet computer and so on, have a shooting function. With development of science and technology, the electronic apparatuses such as a smart phone have more and more powerful shooting function, and as compared with a bulky single lens reflex camera, such electronic apparatuses have advantages such as lightweight, easy operation and so on, and thus users are provided with great convenience.
However, sometimes people take a photo at a relatively slow shutter speed, so as to obtain an image of a motion track of an object. For example, under a normal sunlight condition, in order to express a speed of a moving object (e.g., running water), a shutter speed of a few seconds may be used to take a photo. For another example, when the users desire to obtain an image of a star track at night, a shutter speed of several minutes or even more than ten minutes may be needed. However, the relatively slow shutter speed may cause long exposure time of a sensitive chip, so it is likely to cause overexposure if light is adequate. Although exposure may be reduced in a manner of reducing a photosensitivity (ISO) or an aperture value according to a reciprocity law in photography, generally the photosensitivity may be only minimized to ISO 100, and an adjusting range of the aperture value is limited, too. In particular, for other electronic apparatuses which are not dedicated to shooting, since the shooting function is not a main function thereof, the aperture value may be not adjustable. Moreover, reducing the aperture value may result in enlarging a depth of field, which cannot meet needs of the users for a small depth of field. People can also use a gray mirror to reduce the exposure, but it is required to provide the gray mirror in front of the lens, which may be inconvenient to the users, and gray values of the gray mirror are also difficult to control.